This invention relates generally to the art of earth boring and more particularly to a bearing construction for a rotary earth boring drill bit. The invention is particularly useful on a type of rotary drill bit known in the art as a tri-coned or duo-coned bit. It will be apparent, however, that the invention is applicable to other earth boring bits or the like.
In use, a tri-coned bit is connected at the lower end of a rotary drill string and, as the drill string is rotated, the bit disintegrates the earth formation by compressive failure to form a bore hole. A tri-coned bit includes three aprons that extend downwardly from the main body of the bit and have formed or supported thereon a bearing pin or journal. A cone cutter is mounted on each of the journals for rotation thereon. The cone cutters are provided with teeth or other cutting surfaces that disintegrate the formations as the bit is rotated.
Drill bits of the indicated type are subjected to severe operating conditions as a result of the environment in which they operate and the impact and other loads to which they are subjected during a drilling operation. Failure of the drill bit is costly in applications such as the drilling of bore holes for oil since the entire drill string must be removed to replace the failed drill bit. Since reasonable success has been achieved in improving the cutting structure of the cone cutter to extend its useful life, the result is that the bearings of the drill bits are generally the first part to fail during the drilling operations.
The primary reason for the failure of the prior art bearings is that as wear occurs the bearings become loose. Serious problems then result because (1) a loose bearing does not transfer forces accurately, (2) the teeth of the cutter rub back and forth and wear out without accomplishing compressive failure of the formation, and (3) the loose bearing permits intermittent torsional frequency which is often accompanied by a whiplash type of action.